This research is designed to study the mechanisms by which antibodies directed against surface membrane antigens alter the function of neutrophils and other cells. In particular the role of such interaction in clinical disease in which antineutrophil antibodies are found, is the specific subject of this research. Information will be gathered by several approaches: 1. Investigating the relationship between patching of surface antigen and activation of cellular activities by examining the induction of endocytic activity in erythrocytes of neonates which have been coated with antibody. 2. Screening of patients with neutropenia or history of reaction to neutrophil transfusions using a leukoagglutination assay. 3. Obtaining a xenogenic antineutrophil antibody. 4. Characterizing the effect of purified antibody, antibody Fab fragments and lectins on such neutrophil functions as motility, chemotaxis, adhesion, phagocytosis, and H2O2 production. 5. Characterizing morphologically the binding sites of antibody on the neutrophil membrane. 6. Characterizing the chemical nature of antigenic sites. The purpose of these investigations is to provide an understanding of how antibodies alter target cell function as well as to increase our knowledge of the critical functional components of the neutrophil membrane. Such knowledge will lead to better therapies in autoimmune diseases, as well as to an increase in our ability to manipulate neutrophil cell function in disease and health.